I am new to enzymes. Got a topic to work with tryptophanase. However, the mutant tryptophanase is very unstable and it looses its activity within few hours in the crude extract. Hence, there is problem to purify it in its active form. I would like to know how can I characterize the enzyme in crude extract itself. Any suggestions to improve the stability of the enzyme is highly appreciated.

Are you using full speactrum of broad range proteases in your lysis buffer? how much salt do you have in buffer? characterizing enzyme in very crude extract is of limited value, how about partial characterization using ammonium sulphate or acetone preocipitation?